diff --git a/src/dirty.rs b/src/dirty.rs
index 6dea50e..f73601f 100644
--- a/src/dirty.rs
+++ b/src/dirty.rs
@@ -1,4 +1,5 @@
 use core::ops::{Deref, DerefMut};
+use core::fmt::{Debug, Formatter, Error};
 
 /// Dirty wraps a value of type T with functions similiar to that of a Read/Write
 /// lock but simply sets a dirty flag on write(), reset on read()
@@ -60,3 +61,10 @@ impl<T> Drop for Dirty<T> {
     }
 }
 
+impl<T: Debug> Debug for Dirty<T> {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        let tag = if self.dirty {"Dirty"} else {"Clean"};
+        write!(f, "[{}] {:?}", tag, self.value)
+    }
+}
+
diff --git a/src/sfs.rs b/src/sfs.rs
index 83a2c1f..adb4055 100644
--- a/src/sfs.rs
+++ b/src/sfs.rs
@@ -44,7 +44,6 @@ trait DeviceExt: Device {
 impl DeviceExt for Device {}
 
 type Ptr<T> = Rc<RefCell<T>>;
-type WeakPtr<T> = Weak<RefCell<T>>;
 
 /// inode for sfs
 pub struct INode {
@@ -58,7 +57,7 @@ pub struct INode {
 
 impl Debug for INode {
     fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
-        write!(f, "{:?}", *self.disk_inode)
+        write!(f, "INode {{ id: {}, disk: {:?} }}", self.id, self.disk_inode)
     }
 }
 
@@ -105,7 +104,7 @@ impl INode {
         }
     }
     /// Only for Dir
-    fn get_file_inode_id(&mut self, name: &'static str) -> Option<INodeId> {
+    fn get_file_inode_id(&self, name: &'static str) -> Option<INodeId> {
         (0 .. self.disk_inode.blocks)
             .map(|i| {
                 use vfs::INode;
@@ -153,7 +152,7 @@ impl vfs::INode for INode {
     fn close(&mut self) -> vfs::Result<()> {
         self.sync()
     }
-    fn read_at(&mut self, offset: usize, buf: &mut [u8]) -> vfs::Result<usize> {
+    fn read_at(&self, offset: usize, buf: &mut [u8]) -> vfs::Result<usize> {
         let fs = self.fs.upgrade().unwrap();
 
         let iter = BlockIter {
@@ -171,7 +170,7 @@ impl vfs::INode for INode {
         }
         Ok(buf_offset)
     }
-    fn write_at(&mut self, offset: usize, buf: &[u8]) -> vfs::Result<usize> {
+    fn write_at(&self, offset: usize, buf: &[u8]) -> vfs::Result<usize> {
         let fs = self.fs.upgrade().unwrap();
 
         let iter = BlockIter {
@@ -189,7 +188,7 @@ impl vfs::INode for INode {
         }
         Ok(buf_offset)
     }
-    fn info(&mut self) -> vfs::Result<vfs::FileInfo> {
+    fn info(&self) -> vfs::Result<vfs::FileInfo> {
         Ok(vfs::FileInfo {
             size: self.disk_inode.size as usize,
             mode: 0,
@@ -269,7 +268,7 @@ impl vfs::INode for INode {
 
         Ok(inode)
     }
-    fn loopup(&mut self, path: &'static str) -> vfs::Result<Ptr<vfs::INode>> {
+    fn lookup(&self, path: &'static str) -> vfs::Result<Ptr<vfs::INode>> {
         let fs = self.fs.upgrade().unwrap();
         let info = self.info().unwrap();
         assert_eq!(info.type_, vfs::FileType::Dir);
@@ -288,7 +287,7 @@ impl vfs::INode for INode {
         let type_ = inode.borrow().disk_inode.type_;
         match type_ {
             FileType::File => if rest_path == "" {Ok(inode)} else {Err(())},
-            FileType::Dir => inode.borrow_mut().loopup(rest_path),
+            FileType::Dir => inode.borrow_mut().lookup(rest_path),
             _ => unimplemented!(),
         }
     }
@@ -441,46 +440,43 @@ impl SimpleFileSystem {
         self.super_block.borrow_mut().unused_blocks += 1;
     }
 
+    /// Create a new INode struct, then insert it to self.inodes
+    /// Private used for load or create INode
+    fn _new_inode(&self, id: INodeId, disk_inode: Dirty<DiskINode>) -> Ptr<INode> {
+        let inode = Rc::new(RefCell::new(INode {
+            disk_inode,
+            id,
+            fs: self.self_ptr.clone(),
+        }));
+        self.inodes.borrow_mut().insert(id, inode.clone());
+        inode
+    }
     /// Get inode by id. Load if not in memory.
     /// ** Must ensure it's a valid INode **
     fn get_inode(&self, id: INodeId) -> Ptr<INode> {
         assert!(!self.free_map.borrow().contains(id));
 
-        let mut inodes = self.inodes.borrow_mut();
         // Load if not in memory.
-        if !inodes.contains_key(&id) {
-            let disk_inode = self.device.borrow_mut().load_struct::<DiskINode>(id);
-            let inode = Rc::new(RefCell::new(INode {
-                disk_inode: Dirty::new(disk_inode),
-                id,
-                fs: self.self_ptr.clone(),
-            }));
-            inodes.insert(id, inode.clone());
-            inode
+        if !self.inodes.borrow().contains_key(&id) {
+            let disk_inode = Dirty::new(self.device.borrow_mut().load_struct::<DiskINode>(id));
+            self._new_inode(id, disk_inode)
         } else {
-            inodes.get(&id).unwrap().clone()
+            self.inodes.borrow_mut().get(&id).unwrap().clone()
         }
     }
     /// Create a new INode file
     fn new_inode_file(&self) -> vfs::Result<Ptr<INode>> {
         let id = self.alloc_block().unwrap();
-        Ok(Rc::new(RefCell::new(INode {
-            disk_inode: Dirty::new_dirty(DiskINode::new_file()),
-            id,
-            fs: self.self_ptr.clone(),
-        })))
+        let disk_inode = Dirty::new_dirty(DiskINode::new_file());
+        Ok(self._new_inode(id, disk_inode))
     }
     /// Create a new INode dir
     fn new_inode_dir(&self, parent: INodeId) -> vfs::Result<Ptr<INode>> {
         let id = self.alloc_block().unwrap();
-        let mut inode = INode {
-            disk_inode: Dirty::new_dirty(DiskINode::new_dir()),
-            id,
-            fs: self.self_ptr.clone(),
-        };
-        inode.init_dir(parent).unwrap();
-
-        Ok(Rc::new(RefCell::new(inode)))
+        let disk_inode = Dirty::new_dirty(DiskINode::new_dir());
+        let inode = self._new_inode(id, disk_inode);
+        inode.borrow_mut().init_dir(parent).unwrap();
+        Ok(inode)
     }
 }
 
diff --git a/src/tests.rs b/src/tests.rs
index fe9b131..39fff5c 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -4,6 +4,7 @@ use std::boxed::Box;
 use super::sfs::*;
 use super::vfs::*;
 use super::vfs::INode;
+use std::rc::Rc;
 
 impl Device for File {
     fn read_at(&mut self, offset: usize, buf: &mut [u8]) -> Option<usize> {
@@ -23,14 +24,35 @@ impl Device for File {
     }
 }
 
-#[test]
-fn test() {
+fn _open_sample_file() -> Rc<SimpleFileSystem> {
     let file = File::open("sfs.img")
         .expect("failed to open sfs.img");
-    let sfs = SimpleFileSystem::open(Box::new(file))
-        .expect("failed to create SFS");
+    SimpleFileSystem::open(Box::new(file))
+        .expect("failed to open SFS")
+}
+
+fn _create_new_sfs() -> Rc<SimpleFileSystem> {
+    let file = OpenOptions::new()
+        .read(true).write(true).create(true).open("test.img")
+        .expect("failed to create file");
+    SimpleFileSystem::create(Box::new(file), 16 * 4096)
+}
+
+#[test]
+fn open_sample_file() {
+    _open_sample_file();
+}
+
+#[test]
+fn create_new_sfs() {
+    _create_new_sfs();
+}
+
+#[test]
+fn print_root() {
+    let sfs = _open_sample_file();
     let root = sfs.root_inode();
-    println!("{:?}", root);
+    println!("{:?}", root.borrow());
 
     use super::structs::{DiskEntry, AsBuf};
     use std::mem::uninitialized;
@@ -42,12 +64,28 @@ fn test() {
 }
 
 #[test]
-fn create() {
-    let file = OpenOptions::new()
-        .read(true).write(true).create(true).open("test.img")
-        .expect("failed to create file");
-    let sfs = SimpleFileSystem::create(Box::new(file), 16 * 4096);
+fn create_file() {
+    let sfs = _create_new_sfs();
+    let root = sfs.root_inode();
+    let file1 = root.borrow_mut().create("file1").unwrap();
+
+    assert_eq!(file1.borrow().info().unwrap(), FileInfo {
+        size: 0,
+        type_: FileType::File,
+        mode: 0,
+    });
+
+    sfs.sync().unwrap();
+}
+
+#[test]
+fn lookup() {
+    let sfs = _create_new_sfs();
     let root = sfs.root_inode();
     let file1 = root.borrow_mut().create("file1").unwrap();
+    let found = root.borrow().lookup("file1").expect("lookup not found");
+    println!("{:?}", found.borrow());
+    println!("{:?}", file1.borrow());
+    assert!(Rc::ptr_eq(&found, &file1), "found wrong INode");
     sfs.sync().unwrap();
 }
\ No newline at end of file
diff --git a/src/vfs.rs b/src/vfs.rs
index ebf6746..d5cf004 100644
--- a/src/vfs.rs
+++ b/src/vfs.rs
@@ -2,25 +2,26 @@ use alloc::rc::{Rc, Weak};
 use core::cell::RefCell;
 use core::mem::size_of;
 use core;
+use core::fmt::Debug;
 
 /// Abstract operations on a inode.
-pub trait INode {
+pub trait INode: Debug {
     fn open(&mut self, flags: u32) -> Result<()>;
     fn close(&mut self) -> Result<()>;
-    fn read_at(&mut self, offset: usize, buf: &mut [u8]) -> Result<usize>;
-    fn write_at(&mut self, offset: usize, buf: &[u8]) -> Result<usize>;
-    fn info(&mut self) -> Result<FileInfo>;
+    fn read_at(&self, offset: usize, buf: &mut [u8]) -> Result<usize>;
+    fn write_at(&self, offset: usize, buf: &[u8]) -> Result<usize>;
+    fn info(&self) -> Result<FileInfo>;
     fn sync(&mut self) -> Result<()>;
 //    fn name_file(&mut self) -> Result<()>;
 //    fn reclaim(&mut self) -> Result<()>;
 //    fn try_seek(&mut self, offset: u64) -> Result<()>;
     fn resize(&mut self, len: usize) -> Result<()>;
     fn create(&mut self, name: &'static str) -> Result<Rc<RefCell<INode>>>;
-    fn loopup(&mut self, path: &'static str) -> Result<Rc<RefCell<INode>>>;
+    fn lookup(&self, path: &'static str) -> Result<Rc<RefCell<INode>>>;
 //    fn io_ctrl(&mut self, op: u32, data: &[u8]) -> Result<()>;
 }
 
-#[derive(Debug)]
+#[derive(Debug, Eq, PartialEq)]
 pub struct FileInfo {
     pub size: usize,
     pub mode: u32,